Using "Ctrl-Z" for "undo" in the level editor sounds reasonable. Also "Ctrl-Shift-Z" for "redo" sounds logical and familiar to me.

Regarding "Ctrl-R" for "redo", I'm not totally convinced, as this seems to be handled differently by various programs. (In web browsers, it is "reload", while "redo" in MS Word is invoked by "Ctrl-Y" etc.)

But such "Ctrl style" key shortcuts which are a bit more common nowadays should be quite easy to add to the editor...